Technical Field
The present disclosure relates to the field of semiconductor structures and, more particularly, to bipolar transistors and products that include bipolar transistors.
Description of the Related Technology
Bipolar transistors, such as heterojunction bipolar transistors (HBTs), are implemented in a wide variety of applications. Such bipolar transistors can be formed on semiconductor substrates, such as gallium arsenide (GaAs) substrates. One illustrative application for a bipolar transistor is in a power amplifier system. As technology evolves, specifications for power amplifier systems have become more demanding to meet.
One aspect of power amplifier performance is linearity. Measures of linearity performance can include channel power ratios, such as an adjacent channel power ratio (ACPR1) and an alternative channel power ratio (ACPR2), and/or channel leakage power ratios, such as an adjacent channel leakage power ratio (ACLR1) and an alternative channel leakage power ratio (ACLR2). ACPR2 and ACLR2 can be referred to as second channel linearity measures. ACPR2 and ACLR2 values can correspond at measurements at an offset of about 1.98 MHz from a frequency of interest.
Conventionally, most publications have focused on ACPR1 and ACLR1 linearity measures and little has been published about ACRP2 or ACLR2. Recent ACPR2 and ACLR2 system specifications have been particularly difficult to meet, especially while meeting other system specifications related to RF gain. Accordingly, a need exists for improved linearity in systems that include bipolar transistors, such as power amplifier systems.